Crosslinking systems for hydroxyl polymers

ABSTRACT

Crosslinking systems suitable for use in a polymer melt composition wherein the polymer melt composition comprises a hydroxyl polymer; polymeric structures made from such polymer melt compositions; and processes/methods related thereto are provided.

FIELD OF THE INVENTION

The present invention relates to crosslinking systems suitable for usein a polymer melt composition wherein the polymer melt compositioncomprises a hydroxyl polymer; polymeric structures made from suchpolymer melt composition; and processes/methods related thereto.

BACKGROUND OF THE INVENTION

The crosslinking of hydroxyl polymers is well known, especially in thearea of coatings on substrates and/or particles.

However, the crosslinking of hydroxyl polymers wherein a crosslinkingsystem via a crosslinking agent crosslinks hydroxyl polymers together toproduce a polymeric structure, such as a fiber, a film and/or a foam isnot well known.

The relatively few prior art attempts at producing polymeric structuresof hydroxyl polymers crosslinked together, such as fibers and/or films,have been unsuccessful due, in large part, to the crosslinking systemsutilized in such processes. If a crosslinking system is too reactive,then the hydroxyl polymer may be substantially crosslinked prior to meltprocessing of the hydroxyl polymer and/or the viscosity of the hydroxylpolymer melt composition may increase significantly thus negativelyimpacting, if not completely inhibiting, processing of the polymer meltcomposition into a polymeric structure.

Accordingly, there is a need for a crosslinking system, especially acrosslinking agent, for hydroxyl polymers, especially melt processedhydroxyl polymers, and processes for crosslinking such hydroxyl polymersto form polymeric structures, wherein the processes overcome theproblems described above.

SUMMARY OF THE INVENTION

The present invention fulfills the needs described above by providing acrosslinking system for hydroxyl polymers, especially polyhydroxylpolymers, and processes for crosslinking such hydroxyl polymers.

In one aspect of the present invention, a polymer melt compositioncomprising:

-   -   a. a hydroxyl polymer; and    -   b. a crosslinking system comprising a crosslinking agent capable        of crosslinking the hydroxyl polymer, and optionally a        crosslinking facilitator; and    -   c. optionally, an external plasticizer; and    -   d. optionally a thermoplastic, water-insoluble polymer, is        provided.

In one embodiment, the crosslinking system is capable of crosslinkingthe hydroxyl polymer to form a polymeric structure having an initialtotal wet tensile of at least 1.18 g/cm (3 g/in) and/or at least 1.57g/cm (4 g/in) and/or at least 1.97 g/cm (5 g/in).

In another aspect of the present invention, a polymeric structurederived from a polymer melt composition of the present invention whereinthe processed hydroxyl polymer is crosslinked via the crosslinking agentof the crosslinking system is provided.

In another aspect of the present invention, a polymeric structurecomprising:

-   -   a. a processed hydroxyl polymer; and    -   b. a crosslinking system comprising a crosslinking agent capable        of crosslinking the processed hydroxyl polymer, and optionally a        crosslinking facilitator; and    -   c. optionally, an external plasticizer, and    -   d. optionally a thermoplastic, water-insoluble polymer, is        provided.

In yet another aspect of the present invention, a method for preparing apolymer melt composition comprising the steps of:

-   -   a. providing a melt processed hydroxyl polymer; and    -   b. adding a crosslinking system comprising a crosslinking agent        capable of crosslinking the melt processed hydroxyl polymer to        form the polymer melt composition, is provided.

In still another aspect of the present invention, a method for preparinga polymeric structure comprising the steps of:

-   -   a. providing a polymer melt composition comprising a hydroxyl        polymer and a crosslinking system comprising a crosslinking        agent capable of crosslinking the hydroxyl polymer; and    -   b. processing the polymer melt composition to form the polymeric        structure, is provided.

In still yet another aspect of the present invention, a fibrousstructure comprising one or more polymeric structures in fiber formaccording to the present invention, is provided.

In even yet another aspect of the present invention, a polymericstructure, such as a single- or multi-ply sanitary tissue product,comprising a fibrous structure in accordance with the present invention,is provided.

In even still another aspect of the present invention, a polymericstructure, such as a single- or multi-ply sanitary tissue product,according to the present invention, wherein the polymeric structureexhibits an initial total wet tensile of at least 1.18 g/cm (3 g/in)and/or at least 1.57 g/cm (4 g/in) and/or at least 1.97 g/cm (5 g/in),is provided.

In still yet another aspect of the present invention, a polymericstructure in fiber form produced from the methods of the presentinvention, is provided. The fiber can have an average equivalentdiameter of less than about 50 microns and/or less than about 20 micronsand/or less than about 10 microns and/or less than about 8 micronsand/or less than about 6 microns. “Average equivalent diameter” as usedherein is an equivalent diameter computed as an arithmetic average ofthe actual fiber's diameter measured at 3 or more positions along thefiber's length with an optical microscope. “Equivalent diameter” as usedherein to define a cross-sectional area of an individual fiber of thepresent invention, which cross-sectional area is perpendicular to thelongitudinal axis of the fiber, regardless of whether thiscross-sectional area is circular or non-circular. A cross-sectional areaof any geometrical shape can be defined according to the formula:S=¼πD², where S is the area of any geometrical shape, π=3.14159, and Dis the equivalent diameter. Using a hypothetical example, the fiber'scross-sectional area S of 0.005 square microns having a rectangularshape can be expressed as an equivalent circular area of 0.005 squaremicrons, wherein the circular area has a diameter “D.” Then, thediameter D can be calculated from the formula: S=¼πD², where S is theknown area of the rectangle. In the foregoing example, the diameter D isthe equivalent diameter of the hypothetical rectangular cross-section.Of course, the equivalent diameter of the fiber having a circularcross-section is this circular cross-section's real diameter.

Accordingly, the present invention provides crosslinking systems;polymer melt compositions and/or polymeric structures, especiallyfibrous structures and/or fibers, containing such crosslinking systems;and methods for making same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a schematic side view of a barrel of a twin screw extrudersuitable for use in the present invention.

FIG. 1B is a schematic side view of a screw and mixing elementconfiguration suitable for use in the barrel of FIG. 1A.

FIG. 2 is a schematic side view of a process for synthesizing apolymeric structure in accordance with the present invention.

FIG. 3 is a schematic partial side view of the process of the presentinvention, showing an attenuation zone.

FIG. 4 is a schematic plan view taken along lines 4-4 of FIG. 3 andshowing one possible arrangement of a plurality of extrusion nozzlesarranged to provide polymeric structures of the present invention.

FIG. 5 is a view similar to that of FIG. 4 and showing one possiblearrangement of orifices for providing a boundary air around theattenuation zone.

DETAILED DESCRIPTION OF THE INVENTION Methods of the Present Invention

The methods of the present invention relate to producing polymericstructures from a polymer melt composition comprising a hydroxyl polymerand a crosslinking system.

A. Polymer Melt Composition

“Polymer melt composition” as used herein means a composition thatcomprises a melt processed hydroxyl polymer. “Melt processed hydroxylpolymer” as used herein means any polymer that contains greater than 10%and/or greater than 20% and/or greater than 25% by weight hydroxylgroups and that has been melt processed, with or without the aid of anexternal plasticizer. More generally, melt processed hydroxyl polymersinclude polymers, which by the influence of elevated temperatures,pressure and/or external plasticizers may be softened to such a degreethat they can be brought into a flowable state, and in this conditionmay be shaped as desired.

The polymer melt composition may be a composite containing a blend ofpolymers, wherein at least one is a melt processed hydroxyl polymeraccording to the present invention, and/or fillers both inorganic andorganic, and/or fibers and/or foaming agents.

The polymer melt composition may already be formed or a melt processingstep may need to be performed to convert a raw material hydroxyl polymerinto a melt processed hydroxyl polymer, thus producing the polymer meltcomposition. Any suitable melt processing step known in the art may beused to convert the raw material hydroxyl polymer into the meltprocessed hydroxyl polymer. “Melt processing” as used herein means anyoperation and/or process by which a polymer is softened to such a degreethat it can be brought into a flowable state.

The polymer melt composition may have a shear viscosity, as measuredaccording to the Shear Viscosity of a Polymer Melt CompositionMeasurement Test Method described herein, of from about 1 Pascal·Secondsto about 25 Pascal·Seconds and/or from about 2 Pascal·Seconds to about20 Pascal·Seconds and/or from about 3 Pascal·Seconds to about 10Pascal·Seconds, as measured at a shear rate of 3,000 sec⁻¹ and at theprocessing temperature (50° C. to 100° C.). Additionally, the normalizedshear viscosity of the polymer melt composition of the present inventionmust not increase more than 1.3 times the initial shear viscosity valueafter 70 minutes and/or 2 times the initial shear viscosity value after130 minutes when measured at a shear rate of 3,000 sec⁻¹ according tothe Shear Viscosity Change Test Method described herein.

The polymer melt composition may have a temperature of from about 50° C.to about 100° C. and/or from about 65° C. to about 95° C. and/or fromabout 70° C. to about 90° C. when making fibers from the polymer meltcomposition. The polymer melt composition temperature is generallyhigher when making film and/or foam polymeric structures, as describedbelow.

The pH of the polymer melt composition may be from about 2.5 to about 9and/or from about 3 to about 8.5 and/or from about 3.2 to about 8 and/orfrom about 3.2 to about 7.5.

In one embodiment, a polymer melt composition of the present inventionmay comprise from about 30% and/or 40% and/or 45% and/or 50% to about75% and/or 80% and/or 85% and/or 90% and/or 95% and/or 99.5% by weightof the polymer melt composition of a hydroxyl polymer. The hydroxylpolymer may have a weight average molecular weight greater than about100,000 g/mol prior to crosslinking.

A crosslinking system may be present in the polymer melt compositionand/or may be added to the polymer melt composition before polymerprocessing of the polymer melt composition.

The polymer melt composition may comprise a) from about 30% and/or 40%and/or 45% and/or 50% to about 75% and/or 80% and/or 85% by weight ofthe polymer melt composition of a hydroxyl polymer; b) a crosslinkingsystem comprising from about 0.1% to about 10% by weight of the polymermelt composition of a crosslinking agent; and c) from about 10% and/or15% and/or 20% to about 50% and/or 55% and/or 60% and/or 70% by weightof the polymer melt composition of external plasticizer e.g., water.

The crosslinking system of the present invention may further comprise,in addition to the crosslinking agent, a crosslinking facilitator.

“Crosslinking agent” as used herein means any material that is capableof crosslinking a hydroxyl polymer within a polymer melt compositionaccording to the present.

“Crosslinking facilitator” as used herein means any material that iscapable of activating a crosslinking agent thereby transforming thecrosslinking agent from its unactivated state to its activated state. Inother words, when a crosslinking agent is in its unactivated state, thehydroxyl polymer present in the polymer melt composition refrains fromundergoing unacceptable crosslinking as determined according to theShear Viscosity Change Test Method described herein.

When a crosslinking agent in accordance with the present invention is inits activated state, the hydroxyl polymer present in the polymericstructure may and/or does undergo acceptable crosslinking via thecrosslinking agent as determined according to the Initial Total WetTensile Test Method described herein.

Upon crosslinking the hydroxyl polymer, the crosslinking agent becomesan integral part of the polymeric structure as a result of crosslinkingthe hydroxyl polymer as shown in the following schematic representation:

-   -   Hydroxyl polymer—Crosslinking agent—Hydroxyl polymer

The crosslinking facilitator may include derivatives of the materialthat may exist after the transformation/activation of the crosslinkingagent. For example, a crosslinking facilitator salt being chemicallychanged to its acid form and vice versa.

Nonlimiting examples of suitable crosslinking facilitators include acidshaving a pKa of between 2 and 6 or salts thereof. The crosslinkingfacilitators may be Bronsted Acids and/or salts thereof, such asammonium salts thereof.

In addition, metal salts, such as magnesium and zinc salts, can be usedalone or in combination with Bronsted Acids and/or salts thereof, ascrosslinking facilitators.

Nonlimiting examples of suitable crosslinking facilitators includeacetic acid, benzoic acid, citric acid, formic acid, glycolic acid,lactic acid, maleic acid, phthalic acid, phosphoric acid, succinic acidand mixtures thereof and/or their salts, such as their ammonium salts,such as ammonium glycolate, ammonium citrate and ammonium sulfate.

Additional nonlimiting examples of suitable crosslinking facilitatorsinclude glyoxal bisulfite salts, primary amine salts, such ashydroxyethyl ammonium salts, hydroxypropyl ammonium salt, secondaryamine salts, ammonium toluene sulfonate, ammonium benzene sulfonate andammonium xylene sulfonate.

Synthesis of Polymer Melt Composition

A polymer melt composition of the present invention may be preparedusing a screw extruder, such as a vented twin screw extruder.

A barrel 10 of an APV Baker (Peterborough, England) twin screw extruderis schematically illustrated in FIG. 1A. The barrel 10 is separated intoeight zones, identified as zones 1-8. The barrel 10 encloses theextrusion screw and mixing elements, schematically shown in FIG. 1B, andserves as a containment vessel during the extrusion process. A solidfeed port 12 is disposed in zone 1 and a liquid feed port 14 is disposedin zone 1. A vent 16 is included in zone 7 for cooling and decreasingthe liquid, such as water, content of the mixture prior to exiting theextruder. An optional vent stuffer, commercially available from APVBaker, can be employed to prevent the polymer melt composition fromexiting through the vent 16. The flow of the polymer melt compositionthrough the barrel 10 is from zone 1 exiting the barrel 10 at zone 8.

A screw and mixing element configuration for the twin screw extruder isschematically illustrated in FIG. 1B. The twin screw extruder comprisesa plurality of twin lead screws (TLS) (designated A and B) and singlelead screws (SLS) (designated C and D) installed in series. Screwelements (A-D) are characterized by the number of continuous leads andthe pitch of these leads.

A lead is a flight (at a given helix angle) that wraps the core of thescrew element. The number of leads indicates the number of flightswrapping the core at any given location along the length of the screw.Increasing the number of leads reduces the volumetric capacity of thescrew and increases the pressure generating capability of the screw.

The pitch of the screw is the distance needed for a flight to completeone revolution of the core. It is expressed as the number of screwelement diameters per one complete revolution of a flight. Decreasingthe pitch of the screw increases the pressure generated by the screw anddecreases the volumetric capacity of the screw.

The length of a screw element is reported as the ratio of length of theelement divided by the diameter of the element.

This example uses TLS and SLS. Screw element A is a TLS with a 1.0 pitchand a 1.5 length ratio. Screw element B is a TLS with a 1.0 pitch and a1.0 L/D ratio. Screw element C is a SLS with a ¼ pitch and a 1.0 lengthratio. Screw element D is a SLS and a ¼ pitch and a ½ length ratio.

Bilobal paddles, E, serving as mixing elements, are also included inseries with the SLS and TLS screw elements in order to enhance mixing.Various configurations of bilobal paddles and reversing elements F,single and twin lead screws threaded in the opposite direction, are usedin order to control flow and corresponding mixing time.

In zone 1, the hydroxyl polymer is fed into the solid feed port at arate of 230 grams/minute using a K-Tron (Pitman, N.J.) loss-in-weightfeeder. This hydroxyl polymer is combined inside the extruder (zone 1)with water, an external plasticizer, added at the liquid feed at a rateof 146 grams/minute using a Milton Roy (Ivyland, Pa.) diaphragm pump(1.9 gallon per hour pump head) to form a hydroxyl polymer/water slurry.This slurry is then conveyed down the barrel of the extruder and cooked.Table 1 describes the temperature, pressure, and corresponding functionof each zone of the extruder.

TABLE I Temp. Description Zone (° F.) Pressure of Screw Purpose 1 70 LowFeeding/ Feeding and Mixing Conveying 2 70 Low Conveying Mixing andConveying 3 70 Low Conveying Mixing and Conveying 4 130 Low Pressure/Conveying and Heating Decreased Conveying 5 300 Medium Pressure Cookingat Pressure Generating and Temperature 6 250 High Reversing Cooking atPressure and Temperature 7 210 Low Conveying Cooling and Conveying (withventing) 8 210 Low Pressure Conveying Generating

After the slurry exits the extruder, part of the melt processed hydroxylpolymer is dumped and another part (100 g) is fed into a Zenith®, typePEP II (Sanford N.C.) and pumped into a SMX style static mixer(Koch-Glitsch, Woodridge, Ill.) The static mixer is used to combineadditives such as crosslinking agent, crosslinking facilitator, externalplasticizer, such as water, with the melt processed hydroxyl polymer.The additives are pumped into the static mixer via PREP 100 HPLC pumps(Chrom Tech, Apple Valley Minn.). These pumps provide high pressure, lowvolume addition capability. The polymer melt composition of the presentinvention is ready to be processed by a polymer processing operation.

B. Polymer Processing

“Polymer processing” as used herein means any operation and/or processby which a polymeric structure comprising a processed hydroxyl polymeris formed from a polymer melt composition. Nonlimiting examples ofpolymer processing operations include extrusion, molding and/or fiberspinning. Extrusion and molding (either casting or blown), typicallyproduce films, sheets and various profile extrusions. Molding mayinclude injection molding, blown molding and/or compression molding.Fiber spinning may include spun bonding, melt blowing, rotary spinning,continuous filament producing and/or tow fiber producing.

A “processed hydroxyl polymer” as used herein means any hydroxyl polymerthat has undergone a melt processing operation and a subsequent polymerprocessing operation.

C. Polymeric Structure

The polymer melt composition can be subjected to one or more polymerprocessing operations such that the polymer melt composition isprocessed into a polymeric structure comprising the hydroxyl polymer anda crosslinking system according to the present invention.

“Polymeric structure” as used herein means any physical structure formedas a result of processing a polymer melt composition in accordance withthe present invention. Nonlimiting examples of polymeric structures inaccordance with the present invention include fibers, films and/orfoams.

The crosslinking system via the crosslinking agent crosslinks hydroxylpolymers together to produce the polymeric structure of the presentinvention, with or without being subjected to a curing step. In otherwords, the crosslinking system in accordance with the present inventionacceptably crosslinks, as determined by the Initial Total Wet TensileTest Method described herein, the hydroxyl polymers of a processedpolymer melt composition together via the crosslinking agent to form anintegral polymeric structure. The crosslinking agent is a “buildingblock” for the polymeric structure. Without the crosslinking agent, nopolymeric structure in accordance with the present invention could beformed.

Polymeric structures of the present invention do not include coatingsand/or other surface treatments that are applied to a pre-existing form,such as a coating on a fiber, film or foam. However, in one embodimentof the present invention, a polymeric structure in accordance with thepresent invention may be coated and/or surface treated with thecrosslinking system of the present invention.

Further, in another embodiment, the crosslinking system of the presentinvention may be applied to a pre-existing form as a coating and/orsurface treatment.

In one embodiment, the polymeric structure produced via a polymerprocessing operation may be cured at a curing temperature of from about110° C. to about 215° C. and/or from about 110° C. to about 200° C.and/or from about 120° C. to about 195° C. and/or from about 130° C. toabout 185° C. for a time period of from about 0.01 and/or 1 and/or 5and/or 15 seconds to about 60 minutes and/or from about 20 seconds toabout 45 minutes and/or from about 30 seconds to about 30 minutes.Alternative curing methods may include radiation methods such as UV,e-beam, IR and other temperature-raising methods.

Further, the polymeric structure may also be cured at room temperaturefor days, either after curing at above room temperature or instead ofcuring at above room temperature.

The polymeric structure may exhibit an initial total wet tensile, asmeasured by the Initial Total Wet Tensile Test Method described herein,of at least about 1.18 g/cm (3 g/in) and/or at least about 1.57 g/cm (4g/in) and/or at least about 1.97 g/cm (5 g/in) to about 23.62 g/cm (60g/in) and/or to about 21.65 g/cm (55 g/in) and/or to about 19.69 g/cm(50 g/in).

The polymeric structures of the present invention may include melt spunfibers and/or spunbond fibers, staple fibers, hollow fibers, shapedfibers, such as multi-lobal fibers and multicomponent fibers, especiallybicomponent fibers. The multicomponent fibers, especially bicomponentfibers, may be in a side-by-side, sheath-core, segmented pie, ribbon,islands-in-the-sea configuration, or any combination thereof. The sheathmay be continuous or non-continuous around the core. The ratio of theweight of the sheath to the core can be from about 5:95 to about 95:5.The fibers of the present invention may have different geometries thatinclude round, elliptical, star shaped, rectangular, and other variouseccentricities.

In another embodiment, the polymeric structures of the present inventionmay include a multiconstituent polymeric structure, such as amulticomponent fiber, comprising a hydroxyl polymer of the presentinvention along with a thermoplastic, water-insoluble polymer. Amulticomponent fiber, as used herein, means a fiber having more than oneseparate part in spatial relationship to one another. Multicomponentfibers include bicomponent fibers, which is defined as a fiber havingtwo separate parts in a spatial relationship to one another. Thedifferent components of multicomponent fibers can be arranged insubstantially distinct regions across the cross-section of the fiber andextend continuously along the length of the fiber.

A nonlimiting example of such a multicomponent fiber, specifically abicomponent fiber, is a bicomponent fiber in which the hydroxyl polymerof the present invention represents the core of the fiber and thethermoplastic, water-insoluble polymer represents the sheath, whichsurrounds or substantially surrounds the core of the fiber. The polymermelt composition from which such a polymeric structure is derived mayinclude the hydroxyl polymer and the thermoplastic, water-insolublepolymer.

In another multicomponent, especially bicomponent fiber embodiment, thesheath may comprise a hydroxyl polymer and a crosslinking system havinga crosslinking agent, and the core may comprise a hydroxyl polymer and acrosslinking system having a crosslinking agent. With respect to thesheath and core, the hydroxyl polymer may be the same or different andthe crosslinking agent may be the same or different. Further, the levelof hydroxyl polymer may be the same or different and the level ofcrosslinking agent may be the same or different.

One or more polymeric structures of the present invention may beincorporated into a multi-polymeric structure product, such as a fibrousstructure and/or web, if the polymeric structures are in the form offibers. Such a multi-polymeric structure product may ultimately beincorporated into a commercial product, such as a single- or multi-plysanitary tissue product, such as facial tissue, bath tissue, papertowels and/or wipes, feminine care products, diapers, writing papers,cores, such as tissue cores, and other types of paper products.

Synthesis of Polymeric Structure

Nonlimiting examples of processes for preparing polymeric structures inaccordance with the present invention follow.

i) Fiber Formation

A polymer melt composition is prepared according to the Synthesis of aPolymer Melt Composition described above. As shown in FIG. 2, thepolymer melt composition may be processed into a polymeric structure.The polymer melt composition present in an extruder 102 is pumped to adie 104 using pump 103, such as a Zenith®, type PEP II, having acapacity of 0.6 cubic centimeters per revolution (cc/rev), manufacturedby Parker Hannifin Corporation, Zenith Pumps division, of Sanford, N.C.,USA. The hydroxyl polymer's, such as starch, flow to die 104 iscontrolled by adjusting the number of revolutions per minute (rpm) ofthe pump 103. Pipes connecting the extruder 102, the pump 103, the die104, and optionally a mixer 116 are electrically heated andthermostatically controlled to 65° C.

The die 104 has several rows of circular extrusion nozzles 200 spacedfrom one another at a pitch P (FIG. 3) of about 1.524 millimeters (about0.060 inches). The nozzles 200 have individual inner diameters D2 ofabout 0.305 millimeters (about 0.012 inches) and individual outsidediameters (D1) of about 0.813 millimeters (about 0.032 inches). Eachindividual nozzle 200 is encircled by an annular and divergently flaredorifice 250 formed in a plate 260 (FIGS. 3 and 4) having a thickness ofabout 1.9 millimeters (about 0.075 inches). A pattern of a plurality ofthe divergently flared orifices 250 in the plate 260 correspond to apattern of extrusion nozzles 200. The orifices 250 have a largerdiameter D4 (FIGS. 3 and 4) of about 1.372 millimeters (about 0.054inches) and a smaller diameter D3 of 1.17 millimeters (about 0.046inches) for attenuation air. The plate 260 was fixed so that theembryonic fibers 110 being extruded through the nozzles 200 aresurrounded and attenuated by generally cylindrical, humidified airstreams supplied through the orifices 250. The nozzles can extend to adistance from about 1.5 mm to about 4 mm, and more specifically fromabout 2 mm to about 3 mm, beyond a surface 261 of the plate 260 (FIG.3). As shown in FIG. 5, a plurality of boundary-air orifices 300, isformed by plugging nozzles of two outside rows on each side of theplurality of nozzles, as viewed in plane, so that each of theboundary-layer orifice comprised a annular aperture 250 described hereinabove. Additionally, every other row and every other column of theremaining capillary nozzles are blocked, increasing the spacing betweenactive capillary nozzles

As shown in FIG. 2, attenuation air can be provided by heatingcompressed air from a source 106 by an electrical-resistance heater 108,for example, a heater manufactured by Chromalox, Division of EmersonElectric, of Pittsburgh, Pa., USA. An appropriate quantity of steam 105at an absolute pressure of from about 240 to about 420 kiloPascals(kPa), controlled by a globe valve (not shown), is added to saturate ornearly saturate the heated air at the conditions in the electricallyheated, thermostatically controlled delivery pipe 115. Condensate isremoved in an electrically heated, thermostatically controlled,separator 107. The attenuating air has an absolute pressure from about130 kPa to about 310 kPa, measured in the pipe 115. The polymericstructure fibers 110 being extruded have a moisture content of fromabout 20% and/or from about 25% to about 50% and/or to about 55% byweight. The polymer structure fibers 110 are dried by a drying airstream 109 having a temperature from about 149° C. (about 300° F.) toabout 315° C. (about 600° F.) by an electrical resistance heater (notshown) supplied through drying nozzles 112 and discharged at an anglegenerally perpendicular relative to the general orientation of theembryonic fibers being extruded. The polymeric structure fibers aredried from about 45% moisture content to about 15% moisture content(i.e., from a consistency of about 55% to a consistency of about 85%)and are collected on a collection device 111, such as, for example, amovable foraminous belt.

The process parameters are as follows.

Sample Units Attenuation Air Flow Rate G/min 2500 Attenuation AirTemperature ° C. 93 Attenuation Steam Flow Rate G/min 500 AttenuationSteam Gage Pressure kPa 213 Attenuation Gage Pressure in Delivery kPa 26Pipe Attenuation Exit Temperature ° C. 71 Solution Pump Speed Revs/min35 Solution Flow G/min/hole 0.18 Drying Air Flow Rate g/min 10200 AirDuct Type Slots Air Duct Dimensions mm 356 × 127 Velocity viaPitot-Static Tube M/s 34 Drying Air Temperature at Heater ° C. 260 DryDuct Position from Die mm 80 Drying Duct Angle Relative to Fibersdegrees 0

ii) Foam Formation

The polymer melt composition for foam formation is prepared similarly asfor fiber formation except that the added water content may be less,typically from about 10-21% of the hydroxyl polymer weight. With lesswater to plasticize the hydroxyl polymer, higher temperatures are neededin extruder zones 5-8 (FIG. 1A), typically from about 150-250° C. Alsowith less water available, it may be necessary to add the crosslinkingsystem, especially the crosslinking agent, with the water in zone 1. Inorder to avoid premature crosslinking in the extruder, the polymer meltcomposition pH should be between 7 and 8, achievable by using acrosslinking facilitator e.g., ammonium salt. A die is placed at thelocation where the extruded material emerges and is typically held atabout 160-210° C. Modified high amylose starches (for example greaterthan 50% and/or greater than 75% and/or greater than 90% by weight ofthe starch of amylose) granulated to particle sizes ranging from about400-1500 microns may be used in the present invention. It may also beadvantageous to add a nucleating agent such as microtalc or alkali metalor alkaline earth metal salt such as sodium sulfate or sodium chloridein an amount of about 1-8% of the starch weight. The foam may be shapedinto various forms.

iii) Film Formation

The polymer melt composition for film formation is prepared similarly asfor foam formation except that the added water content may be less,typically 3-15% of the hydroxyl polymer weight and a polyol externalplasticizer such as glycerol is included at about 10-30% of the hydroxylpolymer weight. As with foam formation, zones 5-7 (FIG. 1A) are held atabout 160-210° C., however, the slit die temperature is lower between60-120° C. As with foam formation, the crosslinking system, especiallythe crosslinking agent, may be added along with the water in zone 1 andthe polymer melt composition pH may be between about 7-8 achievable byusing a crosslinking facilitator e.g., ammonium salt.

Hydroxyl Polymers

Hydroxyl polymers in accordance with the present invention include anyhydroxyl-containing polymer that is capable of being melt processed foruse in a polymer melt composition in accordance with the presentinvention.

In one embodiment, the hydroxyl polymer of the present inventionincludes greater than 10% and/or greater than 20% and/or greater than25% by weight hydroxyl moieties.

Nonlimiting examples of hydroxyl polymers in accordance with the presentinvention include polyols, such as starch and starch derivatives,cellulose ether and ester derivatives, various other polysaccharides andpolyvinylalcohols.

The hydroxyl polymer may exhibit a weight average molecular weight offrom about 10,000 to about 40,000,000 g/mol and/or from about 10,000 toabout 10,000,000 g/mol. Higher and lower molecular weight hydroxylpolymers may be used in combination with hydroxyl polymers having the aweight average molecular weight of from about 10,000 to about40,000,000.

A. Starch and Starch Derivatives

Natural starch and/or modified starch-based polymer and/or oligomermaterials, such as modified amylose (represented by Structure I below)and/or modified amylopectin (represented by Structure II below) both ofwhich are described in Kirk-Othmer's Encyclopedia of Chemical Technology4^(th) Edition, Vol. 22, pp. 701-703, starch, generally, is described atpp. 699-719, which are suitable for use as the hydroxyl polymers of thepresent invention can be characterized by the following generalmonomeric structure which makes up the starch polymer, alone or incombination:

wherein each R is selected from the group consisting of R₂, R_(C), and

wherein:

-   -   each R₂ is independently selected from the group consisting of H        and C₁-C₄ alkyl;    -   each R_(C) is

-   -   -   wherein each Z is independently selected from the group            consisting of M, R₂, R_(C), and R_(H);

    -   each R_(H) is independently selected from the group consisting        of C₅-C₂₀ alkyl, C₅-C₇ cycloalkyl, C₇-C₂₀ alkylaryl, C₇-C₂₀        arylalkyl, substituted alkyl, hydroxyalkyl, C₁-C₂₀        alkoxy-2-hydroxyalkyl, C₇-C₂₀ alkylaryloxy-2-hydroxyalkyl,        (R₄)₂N-alkyl, (R₄)₂N-2-hydroxyalkyl, (R₄)₃ N-alkyl, (R₄)₃        N-2-hydroxyalkyl, C₆-C₁₂ aryloxy-2-hydroxyalkyl,

and;

-   -   each R₄ is independently selected from the group consisting of        H, C₁-C₂₀ alkyl, C₅-C₇ cycloalkyl, C₇-C₂₀ alkylaryl, C₇-C₂₀        arylalkyl, aminoalkyl, alkylaminoalkyl, dialkylaminoalkyl,        piperidinoalkyl, morpholinoalkyl, cycloalkylaminoalkyl and        hydroxyalkyl;    -   each R₅ is independently selected from the group consisting of        H, C₁-C₂₀ alkyl, C₅-C₇ cycloalkyl, C₇-C₂₀ alkylaryl, C₇-C₂₀        arylalkyl, substituted alkyl, hydroxyalkyl, (R₄)₂N-alkyl, and        (R₄)₃ N-alkyl;        wherein:        -   M is a suitable cation selected from the group consisting of            Na⁺, K⁺, ½Ca²⁺, ½Mg²⁺, or ⁺NH_(j)R_(k) wherein j and k are            independently from 0 to 4 and wherein j+k is 4 and R in this            formula is any moiety capable of forming a cation, such as            methyl and/or ethyl groups or derivative;        -   each x is from 0 to about 5;        -   each y is from about 1 to about 5; and            provided that:    -   the Degree of Substitution for group R_(H) is between about        0.001 and about 0.1 and/or between about 0.005 and about 0.05        and/or between about 0.01 and about 0.05;    -   the Degree of Substitution for group R_(C) wherein Z is H or M        is between about 0 and about 2.0 and/or between about 0.05 and        about 1.0 and/or between about 0.1 and about 0.5;    -   if any R_(H) bears a positive charge, it is balanced by a        suitable anion; and    -   two R₄'s on the same nitrogen can together form a ring structure        selected from the group consisting of piperidine and morpholine.

The “Degree of Substitution” for group R_(H), which is sometimesabbreviated herein “DS_(RH)”, means the number of moles of group R_(H)components that are substituted per anhydrous glucose unit, wherein ananhydrous glucose unit is a six membered ring as shown in the repeatingunit of the general structure above.

The “Degree of Substitution” for group R_(C), which is sometimesabbreviated herein “DS_(RC)”, means the number of moles of group R_(C)components, wherein Z is H or M, that are substituted per anhydrousD-glucose unit, wherein an anhydrous D-glucose unit is a six memberedring as shown in the repeating unit of the general structures above. Itis understood that in addition to the required number of R_(C)components wherein Z is H or M, there can be additional R_(C) componentswherein Z is a group other than H or M.

A natural starch can be modified chemically or enzymatically, as wellknown in the art. For example, the natural starch can be acid-thinned,hydroxy-ethylated or hydroxy-propylated or oxidized. Though all starchesare potentially useful herein, the present invention can be beneficiallypracticed with high amylopectin natural starches (starches that containgreater than 75% and/or greater than 90% and/or greater than 98% and/orabout 99% amylopectin) derived from agricultural sources, which offerthe advantages of being abundant in supply, easily replenishable andinexpensive. Chemical modifications of starch typically include acid oralkali hydrolysis and oxidative chain scission to reduce molecularweight and molecular weight distribution. Suitable compounds forchemical modification of starch include organic acids such as citricacid, acetic acid, glycolic acid, and adipic acid; inorganic acids suchas hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, boricacid, and partial salts of polybasic acids, e.g., KH₂PO₄, NaHSO₄; groupIa or IIa metal hydroxides such as sodium hydroxide, and potassiumhydroxide; ammonia; oxidizing agents such as hydrogen peroxide, benzoylperoxide, ammonium persulfate, potassium permanganate, hypochloricsalts, and the like; and mixtures thereof.

“Modified starch” is a starch that has been modified chemically orenzymatically. The modified starch is contrasted with a native starch,which is a starch that has not been modified, chemically or otherwise,in any way.

Chemical modifications may also include derivatization of starch byreaction of its hydroxyl groups with alkylene oxides, and other ether-,ester-, urethane-, carbamate-, or isocyanate-forming substances.Hydroxyalkyl, acetyl, or carbamate starches or mixtures thereof can beused as chemically modified starches. The degree of substitution of thechemically modified starch is from 0.05 to 3.0, and more specificallyfrom 0.05 to 0.2. Biological modifications of starch may includebacterial digestion of the carbohydrate bonds, or enzymatic hydrolysisusing enzymes such as amylase, amylopectase, and the like.

Generally, all kinds of natural starches can be used in the presentinvention. Suitable naturally occurring starches can include, but arenot limited to: corn starch, potato starch, sweet potato starch, wheatstarch, sago palm starch, tapioca starch, rice starch, soybean starch,arrow root starch, amioca starch, bracken starch, lotus starch, waxymaize starch, and high amylose corn starch. Naturally occurringstarches, particularly corn starch and wheat starch, can be particularlybeneficial due to their low cost and availability.

In order to generate the required rheological properties for high-speedspinning processes, the molecular weight of the natural, unmodifiedstarch should be reduced. The optimum molecular weight is dependent onthe type of starch used. For example, a starch with a low level ofamylose component, such as a waxy maize starch, disperses rather easilyin an aqueous solution with the application of heat and does notretrograde or recrystallize significantly. With these properties, a waxymaize starch can be used at a weight average molecular weight, forexample in the range of 500,000 g/mol to 40,000,000 g/mol. Modifiedstarches such as hydroxy-ethylated Dent corn starch, which containsabout 25% amylose, or oxidized Dent corn starch tend to retrograde morethan waxy maize starch but less than acid thinned starch. Thisretrogradation, or recrystallization, acts as a physical cross-linkingto effectively raise the weight average molecular weight of the starchin aqueous solution. Therefore, an appropriate weight average molecularweight for a typical commercially available hydroxyethylated Dent cornstarch with 2 mole % hydroxyethylation or oxidized Dent corn starch isfrom about 200,000 g/mol to about 3,000,000 g/mol. For ethoxylatedstarches with higher degrees of ethoxylation, for example ahydroxyethylated Dent corn starch with 3 mole % hydroxyethylation,weight average molecular weights of up to 40,000,000 g/mol may besuitable for the present invention. For acid thinned Dent corn starch,which tends to retrograde more than oxidized Dent corn starch, theappropriate weight average molecular weight is from about 100,000 g/molto about 40,000,000 g/mol.

The weight average molecular weight of starch can be reduced to thedesirable range for the present invention by chain scission (oxidativeor enzymatic), hydrolysis (acid or alkaline catalyzed),physical/mechanical degradation (e.g., via the thermomechanical energyinput of the processing equipment), or combinations thereof.

The natural starch can be hydrolyzed in the presence of an acid catalystto reduce the molecular weight and molecular weight distribution of thecomposition. The acid catalyst can be selected from the group consistingof hydrochloric acid, sulfuric acid, phosphoric acid, citric acid, andany combination thereof Also, a chain scission agent may be incorporatedinto a spinnable starch composition such that the chain scissionreaction takes place substantially concurrently with the blending of thestarch with other components. Non-limiting examples of oxidative chainscission agents suitable for use herein include ammonium persulfate,hydrogen peroxide, hypochlorite salts, potassium permanganate, andmixtures thereof. Typically, the chain scission agent is added in anamount effective to reduce the weight average molecular weight of thestarch to the desirable range. It is found that compositions havingmodified starches in the suitable weight average molecular weight rangeshave suitable shear viscosities, and thus improve processability of thecomposition. The improved processability is evident in lessinterruptions of the process (e.g., reduced breakage, shots, defects,hang-ups) and better surface appearance and strength properties of thefinal product, such as fibers of the present invention.

B. Cellulose and Cellulose Derivatives

Modified cellulose-based polymer and/or oligomer materials, such asmodified cellulose (represented by Structure III below which aresuitable for use as the hydroxyl polymers of the present invention canbe characterized by the following general monomeric structures whichmake up the cellulose and/or cellulose derivative polymers, alone or incombination:

wherein each R is selected from the group consisting of R₂, R_(C), and

wherein:

-   -   each R₂ is independently selected from the group consisting of H        and C₁-C₄ alkyl;    -   each R_(C) is

-   -   -   wherein each Z is independently selected from the group            consisting of M, R₂, R_(C), and R_(H);

    -   each R_(H) is independently selected from the group consisting        of C₅-C₂₀ alkyl, C₅-C₇ cycloalkyl, C₇-C₂₀ alkylaryl, C₇-C₂₀        arylalkyl, substituted alkyl, hydroxyalkyl, C₁-C₂₀        alkoxy-2-hydroxyalkyl, C₇-C₂₀ alkylaryloxy-2-hydroxyalkyl,        (R₄)₂N-alkyl, (R₄)₂N-2-hydroxyalkyl, (R₄)₃ N-alkyl, (R₄)₃        N-2-hydroxyalkyl, C₆-C₁₂ aryloxy-2-hydroxyalkyl,

and;

-   -   each R₄ is independently selected from the group consisting of        H, C₁-C₂₀ alkyl, C₅-C₇ cycloalkyl, C₇-C₂₀ alkylaryl, C₇-C₂₀        arylalkyl, aminoalkyl, alkylaminoalkyl, dialkylaminoalkyl,        piperidinoalkyl, morpholinoalkyl, cycloalkylaminoalkyl and        hydroxyalkyl;    -   each R₅ is independently selected from the group consisting of        H, C₁-C₂₀ alkyl, C₅-C₇ cycloalkyl, C₇-C₂₀ alkylaryl, C₇-C₂₀        arylalkyl, substituted alkyl, hydroxyalkyl, (R₄)₂N-alkyl, and        (R₄)₃ N-alkyl;        wherein:        -   M is a suitable cation selected from the group consisting of            Na⁺, K⁺, ½Ca²⁺, ½Mg²⁺, or ⁺NH_(j)R_(k) wherein j and k are            independently from 0 to 4 and wherein j+k is 4 and R in this            formula is any moiety capable of forming a cation, such as            methyl and/or ethyl groups or derivatives;        -   each x is from 0 to about 5;        -   each y is from about 1 to about 5; and            provided that:    -   the Degree of Substitution for group R_(H) is between about        0.001 and about 0.1 and/or between about 0.005 and about 0.05        and/or between about 0.01 and about 0.05;    -   the Degree of Substitution for group R_(C) wherein Z is H or M        is between about 0 and about 2.0 and/or between about 0.05 and        about 1.0 and/or between about 0.1 and about 0.5;    -   if any R_(H) bears a positive charge, it is balanced by a        suitable anion; and    -   two R₄'s on the same nitrogen can together form a ring structure        selected from the group consisting of piperidine and morpholine.

The “Degree of Substitution” for group R_(H), which is sometimesabbreviated herein “DS_(RH)”, means the number of moles of group R_(H)components that are substituted per anhydrous glucose unit, wherein ananhydrous glucose unit is a six membered ring as shown in the repeatingunit of the general structure above.

The “Degree of Substitution” for group R_(C), which is sometimesabbreviated herein “DS_(RC)”, means the number of moles of group R_(C)components, wherein Z is H or M, that are substituted per anhydrousD-glucose unit, wherein an anhydrous D-glucose unit is a six memberedring as shown in the repeating unit of the general structures above. Itis understood that in addition to the required number of R_(C)components wherein Z is H or M, there can be additional R_(C) componentswherein Z is a group other than H or M.

C. Various Other Polysaccharides

“Polysaccharides” herein means natural polysaccharides andpolysaccharide derivatives or modified polysaccharides. Suitablepolysaccharides include, but are not limited to, gums, arabinans,galactans and mixtures thereof.

The polysaccharides can be extracted from plants, produced by organisms,such as bacteria, fungi, prokaryotes, eukaryotes, extracted from animalsand/or humans. For example, xanthan gum can be produced by Xanthomonascampestris, gellan by Sphingomonas paucimobilis, xyloglucan can beextracted from tamarind seed.

The polysaccharides can be linear, or branched in a variety of ways,such as 1-2, 1-3, 1-4, 1-6, 2-3 and mixtures thereof.

The polysaccharides of the present invention may have a weight averagemolecular weight in the range of from about 10,000 to about 40,000,000and/or from about 10,000 to about 10,000,000 and/or from about 500,000to about 5,000,000, and/or from about 1,000,000 to about 5,000,000g/mol.

The polysaccharide may be selected from the group consisting of:tamarind gum (such as xyloglucan polymers), guar gum, chitosan, chitosanderivatives, locust bean gum (such as galactomannan polymers), and otherindustrial gums and polymers, which include, but are not limited to,Tara, Fenugreek, Aloe, Chia, Flaxseed, Psyllium seed, quince seed,xanthan, gellan, welan, rhamsan, dextran, curdlan, pullulan,scleroglucan, schizophyllan, chitin, hydroxyalkyl cellulose, arabinan(such as sugar beets), de-branched arabinan (such as from sugar beets),arabinoxylan (such as rye and wheat flour), galactan (such as from lupinand potatoes), pectic galactan (such as from potatoes), galactomannan(such as from carob, and including both low and high viscosities),glucomannan, lichenan (such as from icelandic moss), mannan (such asivory nuts), pachyman, rhamnogalacturonan, acacia gum, agar, alginates,carrageenan, chitosan, clavan, hyaluronic acid, heparin, inulin,cellodextrins, and mixtures thereof. These polysaccharides can also betreated (such as enzymatically) so that the best fractions of thepolysaccharides are isolated.

The natural polysaccharides can be modified with amines (primary,secondary, tertiary), amides, esters, ethers, alcohols, carboxylicacids, tosylates, sulfonates, sulfates, nitrates, phosphates andmixtures thereof. Such a modification can take place in position 2, 3and/or 6 of the glucose unit. Such modified or derivatizedpolysaccharides can be included in the compositions of the presentinvention in addition to the natural polysaccharides.

Nonlimiting examples of such modified polysaccharides include: carboxyland hydroxymethyl substitutions (e.g., glucuronic acid instead ofglucose); amino polysaccharides (amine substitution, e.g., glucosamineinstead of glucose); C₁-C₆ alkylated polysaccharides; acetylatedpolysaccharide ethers; polysaccharides having amino acid residuesattached (small fragments of glycoprotein); polysaccharides containingsilicone moieties. Suitable examples of such modified polysaccharidesare commercially available from Carbomer and include, but are notlimited to, amino alginates, such as hexanediamine alginate, aminefunctionalized cellulose-like O-methyl-(N-1,12-dodecanediamine)cellulose, biotin heparin, carboxymethylated dextran, guarpolycarboxylic acid, carboxymethylated locust bean gum, caroxymethylatedxanthan, chitosan phosphate, chitosan phosphate sulfate,diethylaminoethyl dextran, dodecylamide alginate, sialic acid,glucuronic acid, galacturonic acid, mannuronic acid, guluronic acid,N-acetylglucosamine, N-acetylgalactosamine, and mixtures thereof.

The polysaccharide polymers can be linear, like inhydroxyalkylcellulose, the polymer can have an alternating repeat likein carrageenan, the polymer can have an interrupted repeat like inpectin, the polymer can be a block copolymer like in alginate, thepolymer can be branched like in dextran, the polymer can have a complexrepeat like in xanthan. Descriptions of the polymer definitions are givein “An introduction to Polysaccharide Biotechnology”, by M. Tombs and S.E. Harding, T.J.Press 1998.

D. Polyvinylalcohol

Polyvinylalcohols which are suitable for use as the hydroxyl polymers(alone or in combination) of the present invention can be characterizedby the following general formula:

each R is selected from the group consisting of C₁-C₄ alkyl; C₁-C₄ acyl;and x/x+y+z=0.5-1.0.

Crosslinking System

“Crosslinking system” as used herein means a crosslinking system thatcomprises a crosslinking agent and optionally a crosslinking facilitatorwherein a polymer melt composition within which the crosslinking systemis present exhibits less than a 1.3 times normalized shear viscositychange after 70 minutes and/or less than a 2 times normalized shearviscosity change after 130 minutes according to the Shear ViscosityChange Test Method described herein. Crosslinking agents and/orcrosslinking systems that do not satisfy this test methods do not fallwithin the scope of the present invention.

The level and/or type of crosslinking agent, level and/or type ofcrosslinking facilitator, if any, within the crosslinking system of thepresent invention are factors that may impact whether the crosslinkingsystem is unacceptable under the Shear Viscosity Change Test Methodand/or provides acceptable crosslinking of a hydroxyl polymer under theInitial Total Wet Tensile Test Method.

Nonlimiting examples of suitable crosslinking agents include compoundsresulting from alkyl substituted or unsubstituted cyclic adducts ofglyoxal with ureas (Structure V, X═O), thioureas (Structure V, X═S),guanidines (Structure V, X═NH, N-alkyl), methylene diamides (StructureVI), and methylene dicarbamates (Structure VII) and derivatives thereof;and mixtures thereof.

In one embodiment, the crosslinking agent has the following structure:

wherein X is O or S or NH or N-alkyl, and R₁ and R₂ are independently

wherein R₃ and R₈ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl, CH₂OH and mixtures thereof, R₄ isindependently selected from the group consisting of: H, linear orbranched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; and q is 0-10,R_(H) is independently selected from the group consisting of: H, linearor branched C₁-C₄ alkyl, and mixtures thereof.

In one embodiment, R₃, R₈ and R₄ are not all C₁-C₄ alkyl in a singleunit.

In yet another embodiment, only one of R₃, R₈ and R₄ is C₁-C₄ alkyl in asingle unit.

In another embodiment, the crosslinking agent has the followingstructure:

wherein R₂ is independently

wherein R₃ and R₈ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl, CH₂OH and mixtures thereof, R₄ isindependently selected from the group consisting of: H, linear orbranched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; and q is 0-10,R_(H) is independently selected from the group consisting of: H, linearor branched C₁-C₄ alkyl, and mixtures thereof.

In one embodiment, R₃, R₈ and R₄ are not all C₁-C₄ alkyl in a singleunit.

In yet another embodiment, only one of R₃, R₈ and R₄ is C₁-C₄ alkyl in asingle unit.

In still another embodiment, the crosslinking agent has the followingstructure:

wherein R₂ is independently

wherein R₃ and R₈ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl, CH₂OH and mixtures thereof, R₄ isindependently selected from the group consisting of: H, linear orbranched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; and q is 0-10,R_(H) is independently selected from the group consisting of: H, linearor branched C₁-C₄ alkyl, and mixtures thereof.

In one embodiment, R₃, R₈ and R₄ are not all C₁-C₄ alkyl in a singleunit.

In yet another embodiment, only one of R₃, R₈ and R₄ is C₁-C₄ alkyl in asingle unit.

In yet other embodiments, the crosslinking agent has one of thefollowing structures (Structure VIII, IX and X):

wherein X is O or S or NH or N-alkyl, and R₁ and R₂ are independently

wherein R₃ and R₈ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl, CH₂OH and mixtures thereof, R₄ isindependently selected from the group consisting of: H, linear orbranched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; and q is 0-10,R_(H) is independently selected from the group consisting of: H, linearor branched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; y is 1-50; R₅is independently selected from the group consisting of: —(CH₂)_(n)—wherein n is 1-12, —(CH₂CH(OH)CH₂)—,

wherein R₆ and R₇ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl and mixtures thereof, wherein R₆and R₇ cannot both be C₁-C₄ alkyl within a single unit; and z is 1-100.

In one embodiment, R₃, R₈ and R₄ are not all C₁-C₄ alkyl in a singleunit.

In yet another embodiment, only one of R₃, R₈ and R₄ is C₁-C₄ alkyl in asingle unit.

The crosslinking agent may have the following structure:

wherein R₁ and R₂ are independently

wherein R₃ and R₈ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl, CH₂OH and mixtures thereof, R₄ isindependently selected from the group consisting of: H, linear orbranched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; and q is 0-10,R_(H) is independently selected from the group consisting of: H, linearor branched C₁-C₄ alkyl, and mixtures thereof; x is 1-100; y is 1-50; R₅is independently —(CH₂)_(n)— wherein n is 1-12.

In one embodiment, R₃, R₈ and R₄ are not all C₁-C₄ alkyl in a singleunit.

In yet another embodiment, only one of R₃, R₈ and R₄ is C₁-C₄ alkyl in asingle unit.

In even another embodiment, the crosslinking agent has the followingstructure:

wherein R₁ and R₂ are independently

wherein R₃ and R₈ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl, CH₂OH and mixtures thereof, R₄ isindependently selected from the group consisting of: H, linear orbranched C₁-C₄ alkyl, and mixtures thereof; x is 0-100; and q is 0-10,R_(H) is independently selected from the group consisting of: H, linearor branched C₁-C₄ alkyl, and mixtures thereof; x is 1-100; y is 1-50; R₅is independently selected from the group consisting of: —(CH₂)_(n)—wherein n is 1-12, —(CH₂CH(OH)CH₂)—,

wherein R₆ and R₇ are independently selected from the group consistingof: H, linear or branched C₁-C₄ alkyl and mixtures thereof, wherein R₆and R₇ cannot both be C₁-C₄ alkyl within a single unit; and z is 1-100.

In one embodiment, R₃, R₈ and R₄ are not all C₁-C₄ alkyl in a singleunit.

In yet another embodiment, only one of R₃, R₈ and R₄ is C₁-C₄ alkyl in asingle unit.

In one embodiment, the crosslinking agent comprises an imidazolidinone(Structure V, X═O) where R₂═H, Me, Et, Pr, Bu, (CH₂CH₂O)_(p)H,(CH₂CH(CH₃)O)_(p)H, (CH(CH₃)CH₂O)_(p)H where p is 0-100 and R₁=methyl. Acommercially available crosslinking agent discussed above; namely,Fixapret NF from BASF, has R₁=methyl, R₂═H.

In another embodiment, the crosslinking agent comprises animidazolidinone (Structure V, X═O) where R₂═H, Me, Et, Pr, Bu and R₁═H.Dihydroxyethyleneurea (DHEU) comprises an imidazolidinone (Structure V,X═O) where both R₁ and R₂ are H. DHEU can be synthesized according tothe procedure in EP Patent 0 294 007 A1.

Not being bound by theory, the crosslinking system functions by linkinghydroxyl polymer chains together via amidal linkages as depicted in thefollowing structure. After crosslinking the crosslinker is part of thepolymeric structure.

One of ordinary skill in the art understands that in all the formulasabove, the carbons to which the OR₂ moiety is bonded, also are bonded toa H, which is not shown in the structures for simplicity reasons.

Nonlimiting examples of commercially available crosslinking agents whichare not part of the invention because they are unacceptable asdetermined by the Shear Viscosity Change Test Method and/or the InitialTotal Wet Tensile Test Method described herein include Permafresh EFC(available from OMNOVA Solutions, Inc), Fixapret ECO (available fromBASF) and Parez 490 (available from Bayer Corporation).

External Plasticizers

As used herein, an “external plasticizer” is any material thatfacilitates the conversion of a raw material hydroxyl polymer into amelt processed hydroxyl polymer without becoming grafted into the meltprocessed hydroxyl polymer and/or becoming bonded to the melt processedhydroxyl polymer.

An external plasticizer can be used in the present invention todestructure the hydroxyl polymer and enable the hydroxyl polymer toflow, i.e. create a polymer melt composition comprising the hydroxylpolymer. The same external plasticizer may be used to increase meltprocessability or two separate external plasticizers may be used. Theexternal plasticizers may also improve the flexibility of the finalproducts, which is believed to be due to the lowering of the glasstransition temperature of the polymer melt composition by the externalplasticizer. The external plasticizers should be substantiallycompatible with the hydroxyl polymer of the present invention so thatthe external plasticizers may effectively modify the properties of thepolymer melt composition. As used herein, the term “substantiallycompatible” means that when heated to a temperature above the softeningand/or the melting temperature of the polymer melt composition, theexternal plasticizer is capable of forming a substantially homogeneousmixture with the hydroxyl polymer.

The external plasticizer will typically have a weight average molecularweight of less than about 100,000 g/mol.

Nonlimiting examples of useful external plasticizers include water;sugars such as glucose, sucrose, fructose, raffinose, maltodextrose,galactose, xylose, maltose, lactose, mannose erythrose, glycerol,oligoglycerol, and pentaerythritol; sugar alcohols such as erythritol,xylitol, malitol, mannitol and sorbitol; polyols such as ethyleneglycol, propylene glycol, dipropylene glycol, butylene glycol, hexanetriol, triethanolamine, dimethylaminoethanol, glycol glucosides, and thelike, and polymers thereof; and mixtures thereof.

Also useful herein as external plasticizers are poloxomers(polyoxyethylene/polyoxypropylene block copolymers) and poloxamines(polyoxyethylene/polyoxypropylene block copolymers of ethylene diamine).Suitable poloxamers and poloxamines are available as Pluronic® andTetronic® from BASF Corp., Parsippany, N.J., and Synperonic® from ICIChemicals, Wilmington, Del.

Also suitable for use herein are hydrogen bond forming organic compoundswhich do not have hydroxyl group, including urea and urea derivatives;anhydrides of sugar alcohols such as sorbitan; animal proteins such asgelatin; vegetable proteins such as sunflower protein, soybean proteins,cotton seed proteins; and mixtures thereof.

Also suitable for use as external plasticizers are aliphatic polymericacids such as polyethylene acrylic acid, polyethylene maleic acid,polybutadiene acrylic acid, poly butadiene maleic acid, polypropyleneacrylic acid, polypropylene maleic acid, and other hydrocarbon basedacids. Especially useful are polyacrylic acids, polyacrylic-co-maleicacids and polymaleic acids, which may be neutralized withtriethanolamine to different degrees of neutralization.

All of the external plasticizers may be used alone or in combinationwith other external plasticizers.

Thermoplastic, Water-Insoluble Polymer

“Thermoplastic, water-insoluble polymer” include water-insolublepolymers which by the influence of elevated temperatures, pressureand/or plasticizers may be softened to such a degree that they can bebrought into a flowable state, and in this condition may be shaped asdesired.

Suitable melting temperatures of the thermoplastic, water-insolublepolymers are from about 80° to about 180° C. and/or from about 90° toabout 150° C. Thermoplastic polymers having a melting temperature above190° C. may be used if plasticizers or diluents are used to lower theobserved melting temperature. In one aspect of the present invention, itmay be desired to use a thermoplastic polymer having a glass transitiontemperature of less than 0° C. Polymers having this low glass transitiontemperature include polypropylene, polyethylene, ethylene acrylic acid,and others.

Thermoplastic, water-insoluble polymers may include polypropylene,polyethylene, polyamides, ethylene acrylic acid, polyolefin carboxylicacid copolymers, polyesters, and combinations thereof.

The weight average molecular weight of the thermoplastic,water-insoluble polymer can be sufficiently high to enable entanglementbetween polymer molecules and yet low enough to be melt spinnable. Formelt spinning, thermoplastic, water-insoluble polymers may exhibitweight average molecular weights below 500,000 g/mol and/or from about5,000 g/mol to about 400,000 g/mol and/or from about 5,000 g/mol toabout 300,000 g/mol and/or from about 10,000 g/mol to about 200,000g/mol.

Typically, when present in the polymer melt compositions and/orpolymeric structures of the present invention, the thermoplastic,water-insoluble polymers are present in an amount of from about 1% toabout 99% and/or from about 10% to about 80% and/or from about 30% toabout 70% and/or from about 40% to about 60%, by weight of the polymermelt composition and/or polymeric structure.

Test Methods of the Present Invention Method A. Shear Viscosity ChangeTest Method

Viscosities of three samples of a single polymer melt compositioncomprising a crosslinking system to be tested are measured by fillingthree separate 60 cc syringes; the shear viscosity of one sample ismeasured immediately (initial shear viscosity) (it takes about 10minutes from the time the sample is placed in the rheometer to get thefirst reading) according to the Shear Viscosity of a Polymer MeltComposition Measurement Test Method. If the initial shear viscosity ofthe first sample is not within the range of 5-8 Pascal·Seconds asmeasured at a shear rate of 3,000 sec-1, then the single polymer meltcomposition has to be adjusted such that the single polymer meltcomposition's initial shear viscosity is within the range of 5-8Pascal·Seconds as measured at a shear rate of 3,000 sec-1 and this ShearViscosity Change Test Method is then repeated. Once the initial shearviscosity of the polymer melt composition is within the range of 5-8Pascal·Seconds as measured at a shear rate of 3,000 sec-1, then theother two samples are measured by the same test method after beingstored in a convection oven at 80° C. for 70 and 130 minutes,respectively. The shear viscosity at 3000 sec-1 for the 70 and 130minute samples is divided by the initial shear viscosity to obtain anormalized shear viscosity change for the 70 and 130 minute samples. Ifthe normalized shear viscosity change is 1.3 times or greater after 70minutes and/or is 2 times or greater after 130 minutes, then thecrosslinking system within the polymer melt composition is unacceptable,and thus is not within the scope of the present invention. However, ifthe normalized shear viscosity change is less than 1.3 times after 70minutes and/or is less than 2 times after 130 minutes, then thecrosslinking system is not unacceptable, and thus it is within the scopeof the present invention with respect to polymer melt compositionscomprising the crosslinking system. The crosslinking system may bedetermined to be acceptable with respect to polymeric structures derivedfrom polymer melt compositions comprising the crosslinking system asdetermined by the Initial Total Wet Tensile Test Method.

The normalized shear viscosity changes may be less than 1.2 times after70 minutes and/or less than 1.7 times after 130 minutes and/or less than1.1 times after 70 minutes and/or less than 1.4 times after 130 minutes.

Nonlimiting examples of crosslinking systems added to a polymer meltcomposition comprising about 55% acid-thinned, hydroxyethylated starch(Ethylex 2025 commercially available from A. E. Staley) and the balancewater prepared according to the present invention, measured by this testmethod include the following (concentrations of crosslinking agent andcrosslinking facilitator are calculated as a % of the starch weightbased on the acid form):

Norm. Norm. Norm. Agent Facilitator Change Change Change Agent LevelFacilitator Level (10 min) (70 min.) (130 min.) DHEU 2.5% Ammonium 1.00%1 1.07 — glycolate DHEU 2.5% Ammonium 5.00% 1 0.96 1.03 lactate DHEU2.06%  Citric acid 0.40% 1 1.15 1.58 DHEU 2.5% Glycolic 1.00% 1 CNR —acid Perma- 2.13%  Citric acid 0.62% 1 1.73 CNR fresh EFC *CNR meansthat the polymer melt composition could not be ran due to its “solid”state.

Method B. Initial Total Wet Tensile Test Method

An electronic tensile tester (Thwing-Albert EJA Materials Tester,Thwing-Albert Instrument Co., 10960 Dutton Rd., Philadelphia, Pa.,19154) is used and operated at a crosshead speed of 4.0 inch (about10.16 cm) per minute and a gauge length of 1.0 inch (about 2.54 cm),using a strip of a polymeric structure of 1 inch wide and a lengthgreater than 3 inches long. The two ends of the strip are placed in theupper jaws of the machine, and the center of the strip is placed arounda stainless steel peg (0.5 cm in diameter). After verifying that thestrip is bent evenly around the steel peg, the strip is soaked indistilled water at about 20° C. for a soak time of 5 seconds beforeinitiating cross-head movement. The initial result of the test is anarray of data in the form load (grams force) versus crossheaddisplacement (centimeters from starting point).

The sample is tested in two orientations, referred to here as MD(machine direction, i.e., in the same direction as the continuouslywound reel and forming fabric) and CD (cross-machine direction, i.e.,90° from MD). The MD and CD wet tensile strengths are determined usingthe above equipment and calculations in the following manner:

Initial Total Wet Tensile=ITWT (g_(f)/inch)=Peak Load_(MD) (g_(f))/2(inch_(width))+Peak Load_(CD) (g_(f))/2 (inch_(width))

The Initial Total Wet Tensile value is then normalized for the basisweight of the strip from which it was tested. The normalized basisweight used is 36 g/m², and is calculated as follows:

Normalized {ITWT}={ITWT}*36 (g/m²)/Basis Weight of Strip (g/m²)

If the initial total wet tensile of a polymeric structure comprising acrosslinking system of the present invention is at least 1.18 g/cm (3g/in) and/or at least 1.57 g/cm (4 g/in) and/or at least 1.97 g/cm (5g/in), then the crosslinking system is acceptable and is within thescope of the present invention. The initial total wet tensile may beless than or equal to about 23.62 g/cm (60 g/in) and/or less than orequal to about 21.65 g/cm (55 g/in) and/or less than or equal to about19.69 g/cm (50 g/in).

Method C. Shear Viscosity of a Polymer Melt Composition Measurement TestMethod

The shear viscosity of a polymer melt composition comprising acrosslinking system is measured using a capillary rheometer, GoettfertRheograph 6000, manufactured by Goettfert USA of Rock Hill S.C., USA.The measurements are conducted using a capillary die having a diameter Dof 1.0 mm and a length L of 30 mm (i.e., L/D=30). The die is attached tothe lower end of the rheometer's 20 mm barrel, which is held at a dietest temperature of 75° C. A preheated to die test temperature, 60 gsample of the polymer melt composition is loaded into the barrel sectionof the rheometer. Rid the sample of any entrapped air. Push the samplefrom the barrel through the capillary die at a set of chosen rates1,000-10,000 seconds⁻¹. An apparent shear viscosity can be calculatedwith the rheometer's software from the pressure drop the sampleexperiences as it goes from the barrel through the capillary die and theflow rate of the sample through the capillary die. The log (apparentshear viscosity) can be plotted against log (shear rate) and the plotcan be fitted by the power law, according to the formula η=Kγ^(n-1),wherein K is the material's viscosity constant, n is the material'sthinning index and γ is the shear rate. The reported apparent shearviscosity of the composition herein is calculated from an interpolationto a shear rate of 3,000 sec⁻¹ using the power law relation.

Method D. Water Content of a Polymer Melt Composition

A weighed sample of a polymer melt composition (4-10 g) is placed in a120° C. convection oven for 8 hours. The sample is reweighed afterremoving from the oven. The % weight loss is recorded as the watercontent of the melt.

Method E. Polymer Melt Composition pH

A polymer melt composition pH is determined by adding 25 mL of thepolymer melt composition to 100 mL of deionized water, stirring with aspatula for 1 min and measuring the pH.

Method F. Weight Average Molecular Weight

The weight average molecular weight (Mw) of a material, such as ahydroxyl polymer is determined by Gel Permeation Chromatography (GPC)using a mixed bed column. A high performance liquid chromatograph (HPLC)having the following components: Millenium®, Model 600E pump, systemcontroller and controller software Version 3.2, Model 717 Plusautosampler and CHM-009246 column heater, all manufactured by WatersCorporation of Milford, Mass., USA, is utilized. The column is a PL gel20 μm Mixed A column (gel molecular weight ranges from 1,000 g/mol to40,000,000 g/mol) having a length of 600 mm and an internal diameter of7.5 mm and the guard column is a PL gel 20 μm, 50 mm length, 7.5 mm ID.The column temperature is 55° C. and the injection volume is 200 μL. Thedetector is a DAWN® Enhanced Optical System (EOS) including Astra®software, Version 4.73.04 detector software, manufactured by WyattTechnology of Santa Barbara, Calif., USA, laser-light scatteringdetector with K5 cell and 690 nm laser. Gain on odd numbered detectorsset at 101. Gain on even numbered detectors set to 20.9. WyattTechnology's Optilab® differential refractometer set at 50° C. Gain setat 10. The mobile phase is HPLC grade dimethylsulfoxide with 0.1% w/vLiBr and the mobile phase flow rate is 1 mL/min, isocratic. The run timeis 30 minutes.

A sample is prepared by dissolving the material in the mobile phase atnominally 3 mg of material/1 mL of mobile phase. The sample is cappedand then stirred for about 5 minutes using a magnetic stirrer. Thesample is then placed in an 85° C. convection oven for 60 minutes. Thesample is then allowed to cool undisturbed to room temperature. Thesample is then filtered through a 5 μm Nylon membrane, type Spartan-25,manufactured by Schleicher & Schuell, of Keene, N.H., USA, into a 5milliliter (mL) autosampler vial using a 5 mL syringe.

For each series of samples measured (3 or more samples of a material), ablank sample of solvent is injected onto the column. Then a check sampleis prepared in a manner similar to that related to the samples describedabove. The check sample comprises 2 mg/mL of pullulan (PolymerLaboratories) having a weight average molecular weight of 47,300 g/mol.The check sample is analyzed prior to analyzing each set of samples.Tests on the blank sample, check sample, and material test samples arerun in duplicate. The final run is a run of the blank sample. The lightscattering detector and differential refractometer is run in accordancewith the “Dawn EOS Light Scattering Instrument Hardware Manual” and“Optilab® DSP Interferometric Refractometer Hardware Manual,” bothmanufactured by Wyatt Technology Corp., of Santa Barbara, Calif., USA,and both incorporated herein by reference.

The weight average molecular weight of the sample is calculated usingthe detector software. A dn/dc (differential change of refractive indexwith concentration) value of 0.066 is used. The baselines for laserlight detectors and the refractive index detector are corrected toremove the contributions from the detector dark current and solventscattering. If a laser light detector signal is saturated or showsexcessive noise, it is not used in the calculation of the molecularmass. The regions for the molecular weight characterization are selectedsuch that both the signals for the 90°□detector for the laser-lightscattering and refractive index are greater than 3 times theirrespective baseline noise levels. Typically the high molecular weightside of the chromatogram is limited by the refractive index signal andthe low molecular weight side is limited by the laser light signal.

The weight average molecular weight can be calculated using a “firstorder Zimm plot” as defined in the detector software. If the weightaverage molecular weight of the sample is greater than 1,000,000 g/mol,both the first and second order Zimm plots are calculated, and theresult with the least error from a regression fit is used to calculatethe molecular mass. The reported weight average molecular weight is theaverage of the two runs of the material test sample.

Method G. Relative Humidity

Relative humidity is measured using wet and dry bulb temperaturemeasurements and an associated psychometric chart. Wet bulb temperaturemeasurements are made by placing a cotton sock around the bulb of athermometer. Then the thermometer, covered with the cotton sock, isplaced in hot water until the water temperature is higher than ananticipated wet bulb temperature, more specifically, higher than about82° C. (about 180° F.). The thermometer is placed in the attenuating airstream, at about 3 millimeters (about ⅛ inch) from the extrusion nozzletips. The temperature will initially drop as the water evaporates fromthe sock. The temperature will plateau at the wet bulb temperature andthen will begin to climb once the sock loses its remaining water. Theplateau temperature is the wet bulb temperature. If the temperature doesnot decrease, then the water is heated to a higher temperature. The drybulb temperature is measured using a 1.6 mm diameter J-type thermocoupleplaced at about 3 mm downstream from the extrusion nozzle tip.

Based on a standard atmospheric psychometric chart or an Excel plug-in,such as for example, “MoistAirTab” manufactured by ChemicaLogicCorporation, a relative humidity is determined. Relative Humidity can beread off the chart, based on the wet and dry bulb temperatures.

Method H. Air Velocity

A standard Pitot tube is used to measure the air velocity. The Pitottube is aimed into the air stream, producing a dynamic pressure readingfrom an associated pressure gauge. The dynamic pressure reading, plus adry bulb temperature reading is used with the standard formulas togenerate an air velocity. A 1.24 mm (0.049 inches) Pitot tube,manufactured by United Sensor Company of Amherst, N.H., USA, isconnected to a hand-held digital differential pressure gauge (manometer)for the velocity measurements.

Method I. Basis Weight Measurement

The basis weight of each polymeric structure in the form of a fibrousstructure is measured prior to dry or wet tensile testing. This isperformed by first cutting the polymeric structure using a one-inchstrip cutter (JDC Precision Sample Cutter, Thwing-Albert InstrumentCompany, Model#JDC 1-10), thereby accurately producing a sample strip of1 inch width. The length of the cut strip depends on the test, and ismeasured accurate to +/−0.05 cm. The mass of each strip is then measuredusing a mass balance with precision to 0.0001 gram. The basis weight isthen calculated as follows:

Basis Weight (grams/meter²)=mass (g)/(length (cm)*2.54 cm/10000 (m²/cm²)

Method J. Fiber Diameters

A polymeric structure comprising fibers of appropriate basis weight(approximately 5 to 20 grams/square meter) is cut into a rectangularshape, approximately 20 mm by 35 mm. The sample is then coated using aSEM sputter coater (EMS Inc, Pa., USA) with gold so as to make thefibers relatively opaque. Typical coating thickness is between 50 and250 nm. The sample is then mounted between two standard microscopeslides and compressed together using small binder clips. The sample isimaged using a 10× objective on an Olympus BHS microscope with themicroscope light-collimating lens moved as far from the objective lensas possible. Images are captured using a Nikon D1 digital camera. AGlass microscope micrometer is used to calibrate the spatial distancesof the images. The approximate resolution of the images is 1 μm/pixel.Images will typically show a distinct bimodal distribution in theintensity histogram corresponding to the fibers and the background.Camera adjustments or different basis weights are used to achieve anacceptable bimodal distribution. Typically 10 images per sample aretaken and the image analysis results averaged.

The images are analyzed in a similar manner to that described by B.Pourdeyhimi, R. and R. Dent in “Measuring fiber diameter distribution innonwovens” (Textile Res. J. 69(4) 233-236, 1999). Digital images areanalyzed by computer using the MATLAB (Version. 6.1) and the MATLABImage Processing Tool Box (Version 3.)The image is first converted intoa grayscale. The image is then binarized into black and white pixelsusing a threshold value that minimizes the intraclass variance of thethresholded black and white pixels. Once the image has been binarized,the image is skeltonized to locate the center of each fiber in theimage. The distance transform of the binarized image is also computed.The scalar product of the skeltonized image and the distance mapprovides an image whose pixel intensity is either zero or the radius ofthe fiber at that location. Pixels within one radius of the junctionbetween two overlapping fibers are not counted if the distance theyrepresent is smaller than the radius of the junction. The remainingpixels are then used to compute a length-weighted histogram of fiberdiameters contained in the image.

EXAMPLE 1 Nonlimiting Example of a Polymeric Structure Derived from aPolymer Melt Composition of the Present Invention

A polymer melt composition comprising Penfilm 162 starch from PenfordProducts, Cedar Rapids, Iowa is prepared according to the presentinvention. Water is added to the static mixer to adjust the starchconcentration of the polymer melt composition to about 55%. DHEU andammonium citrate are added to the static mixer to achieve theconcentrations of 6.28% and 0.39% (concentrations are calculated as a %of the starch weight), respectively.

Fibers are formed from the polymer melt composition in accordance withthe present invention. The fibers are collected in a manner such thatthe fibers form a fibrous web. The fibrous web is then placed in aconvection oven and cured at 150° C. for 30 minutes. The cured webs arecharacterized by basis weight, wet tensile and fiber diameter accordingto the Test Methods described herein. Prior to testing, samples areconditioned overnight at a relative humidity of 48% to 50% and within atemperature range of 22° C. to 24° C. The cured web exhibited a basisweight of 34.8 g/m², a normalized initial total wet tensile of 14.84g/cm (37.7 g/in) and a fiber diameter of 10.8 μm.

All documents cited in the Detailed Description of the Invention are, inrelevant part, incorporated herein by reference; the citation of anydocument is not to be construed as an admission that it is prior artwith respect to the present invention.

While particular embodiments of the present invention have beenillustrated and described, it would be obvious to those skilled in theart that various other changes and modifications can be made withoutdeparting from the spirit and scope of the invention. It is thereforeintended to cover in the appended claims all such changes andmodifications that are within the scope of this invention.

What is claimed is:
 1. A fibrous structure comprising a plurality ofhydroxyl polymer fibers produced from a polymer melt compositioncomprising one or more hydroxyl polymers and one or more externalplasticizers, wherein the fibrous structure exhibits an initial totalwet tensile of at least 1.18 g/cm.
 2. The fibrous structure according toclaim 1 wherein the fibrous structure exhibits an initial total wettensile of at least 1.57 g/cm.
 3. The fibrous structure according toclaim 2 wherein the fibrous structure exhibits an initial total wettensile of at least 1.97 g/cm.
 4. The fibrous structure according toclaim 1 wherein the hydroxyl polymer is selected from the groupconsisting of: polyvinyl alcohol, chitosan, chitosan derivatives,cellulose derivatives, starch, starch derivatives, gums, arabinans,galactans and mixtures thereof.
 5. The fibrous structure according toclaim 1 wherein the hydroxyl polymer has a weight average molecularweight of from about 10,000 to about 40,000,000 g/mol.
 6. The fibrousstructure according to claim 1 wherein at least one of the hydroxylpolymer fibers comprises a crosslinking system comprising a crosslinkingagent.
 7. The fibrous structure according to claim 6 wherein thecrosslinking system further comprises a crosslinking facilitator.
 8. Thefibrous structure according to claim 7 wherein the crosslinkingfacilitator comprises an acid having a pKa of between 2 and 6 or a saltthereof.
 9. The fibrous structure according to claim 8 wherein the acidcomprises a Bronsted Acid.
 10. The fibrous structure according to claim8 wherein the salt comprises an ammonium salt.
 11. The fibrous structureaccording to claim 7 wherein the crosslinking facilitator is selectedfrom the group consisting of: acetic acid, benzoic acid, citric acid,formic acid, phosphoric acid, succinic acid, glycolic acid, lactic acid,maleic acid, phthalic acid and salts thereof, and mixtures thereof. 12.The fibrous structure according to claim 1 wherein at least one of thehydroxyl polymer fibers comprises a pH adjusting agent.
 13. The fibrousstructure according to claim 1 wherein at least one of the hydroxylpolymer fibers exhibits a fiber diameter of less than about 50 μm. 14.The fibrous structure according to claim 1 wherein at least one of thehydroxyl polymer fibers is free of thermoplastic, water-insolublepolymers.
 15. The fibrous structure according to claim 1 wherein atleast one of the hydroxyl polymer fibers is a multi-component fiber. 16.The fibrous structure according to claim 15 wherein the multi-componentfiber is a bicomponent fiber.
 17. The fibrous structure according toclaim 16 wherein the bicomponent fiber is a core/sheath bicomponentfiber.
 18. The fibrous structure according to claim 1 wherein at leastone of the hydroxyl polymer fibers is a meltblown fiber.
 19. The fibrousstructure according to claim 1 wherein at least one of the hydroxylpolymer fibers is a spunbond fiber.
 20. A sanitary tissue productcomprising a fibrous structure according to claim 1.